It is desirable to have a musical instrument that can be played skillfully without extensive practice or development of a high order of dexterity. Such instruments are particularly useful for vocal accompaniment where chords are all that is needed for inspiring an interest in music in students where the use of conventional instruments is discouraging because long hours of practice do not produce perceptible results. On a strummed instrument, such as a guitar, a great deal of skill and dexterity are needed to place the fingers properly for chords and to move them from one chord holding to another rapidly enough to keep time with the beat of the music.
Instruments such as Autoharps have been devised which provide a keyboard along with strummed strings. Chords can be held on an Autoharp without much difficulty because depressing a key actuates a mechanical device that damps a number of strings so that only those needed to produce that chord can be heard. Instruments such as Autoharps, however, must be tuned, and the tone quality available is limited by the structure of the instrument itself. Additionally, there are mechanical limits to how complex the chord can be.
Other instruments have been devised where the sound source is extrinsic to the instrument, and, accordingly, the quality of the tone is not dependent on the structure of the instrument itself. These instruments typically employ a keyboard which actuates an audio system that places the extrinsic sound source into the circuit only when its key is depressed. Extrinsic sound sources are known and are such things as synthesizers, continuous magnetic tapes where one tape is employed for each note and is recorded from a high quality instrument such as an organ or a piano or is produced by an oscillator that is not a musical instrument. Regardless of how good the quality of the extrinsic sound source may be, the music from such instruments characteristically sounds flat. The total volume of such instruments may be varied, but the decay of volume typical of the sound of a plucked string cannot be duplicated for each note in a chord, nor can chords be struck with some notes at higher volume than others. To duplicate these plucked string sounds by the use of volume control would require far more skill and dexterity than playing an instrument itself, if indeed it could be done at all.